A moderate amount of g-phase precipitates in Ni-Fe-Ga ferromagnetic shape memory alloy can drastically improve its toughness. The martensitic transformation temperature, the microstructure and the crystal structure of the complicated alloys Ni50+xFe25-xGa25 (x=3, 4.5, 6) were investigated by DSC, XRD, SEM and TEM techniques. The results showed that the martensitic transformation temperature Tm went up along with the increasing Ni content; the Ni56Fe19Ga25 alloy exhibited a microstructure composed of fine and clear martensite lathes of several martensitic variants in different orientation. The 6M+14M mixed martensite and g-phases were detected in the Ni56Fe19Ga25 alloy by XRD and TEM. Among the investigated alloys, the Ni56Fe19Ga25 alloy had not only the most appropriate martensitic transformation temperature for practical application, but also the suitable crystal structure for facilitating the magnetostrictive strain.
Ti6Al4V substrate was pretreated by anodic oxidation and then hydroxyapatite coatings were deposited on the oxidized titanium surface by hydrothermal-electrochemical method. The effect of oxidation voltage on the phase composition, surface morphology, wettability and roughness of anodic films, as well as on the phase composition, micro-morphology and bioactivity of HA coatings were investigated. The results show that: after anodic oxidation the titanium alloy is covered by TiO2 porous oxide film consisted of rutile and anatase when the voltage is higher than 110 V. The pore size of the titania layer increases with the increase of the anodic voltage and the alloy after anodic oxidation by 120 V has good wettability and the roughness is about Ra=0.56 μm. The HA coatings formed by hydrothermal-electrochemical deposition exhibits a layered structure with a preferential orientation (002) for several of oxidation voltage. The crystallinity of HA increases with anodic oxidation voltage up to 120 V and then decreases. The hydroxyapatite-TiO2 coating deposited on the alloy which had been anodic-oxidized by 120 V has better bioactivity.
The isothermal and cyclic oxidation behavior of GH3535 superalloy in air at 700oC and 900oC were investigated by using TGA method. The results show that GH3535 alloy has a good oxidation resistance to isothermal oxidation at 700℃and 900℃. But the alloy shows a worse resistance to cyclic oxidization, especially when cyclic oxidation at 900 oC the alloy suffered from accelerated oxidation with rather severe spallation of oxide scales. The X-ray and EDS analysis show that the formed oxide scale consists mainly of Cr2O3, NiMn2O4 and FeCr2O4 during isothermal oxidation. However, oxide products such as MoO2, NiFe2O4, NiCr2O4, NiMn2O4, and NiMoO4 can be detected after cyclic oxidation. The oxidation resistance of the alloy decrease noticeably because of the cracking and spallation of the protective oxide scale as well as the continuous participant of Mo in the oxidation process.
The nanocomposites of polyurethane (PU)/oxidized grapheme (GO) were in-situ prepared by a two step process, i.e. firstly the oxidized graphene (GO) and 4, 4’-diphenylmethane diisocyanate (MDI) were fully reacted, and then polyether polyol and trimethylolpropane were further added to synthesize the nanocomposites. The mechanical property and thermal stability of the nanocomposites were investigated by wide-angle x-ray diffractormetry (WAXD), tensile test machine, TGA and SEM. The GOs evenly dispersed and no aggregation was found in PU matrix for the PU/GO nanocomposites with 0.2 % GO. However, the aggregation of GOs appeared and increased with the increasing GO content. The aggregation of GOs was harmful to the mechanical property and thermal stability of the PU/GO nanocomposites. The nanocomposites of PU/0.2% GO show the best mechanical property and thermal stability. The reduced nanocomposites of PU/GO (named as PU/rGO) were prepared by an in-situ reduction process in a solution of sodium hydrosulfite and sodium hydroxide. It follows that the GOs in the PU matrix could be partly reduced; however such partly reduction of GOs would decline the mechanical property, while enhance the thermal stability of the nanocomposites.
The effect of isothermal heat treatment on the microstructure evolution of semi-solid AZ91D magnesium alloy was investigated. The results show that the roundness of the primary α-Mg phase increases with the increasing temperature and time. The microstructure evolution of the semi-solid AZ91D experiences three stages during isothermal heat treatment process, i.e. the structure separation, spheroidization and final coarsening. The liquid phase of semi-solid alloy has three types, namely, the molten pool, the “entrapped liquid” pool and the liner liquid film which separates two neighbor particles. The solid phase has two types, namely, the primary α-Mg particles and the α-Mg phase formed in the second solidification.
The effect of indirect extrusion process and T76 heat treatment on microstructure evolution and mechanical properties of the spray formed 7055 alloy was investigated by means of optical microscopy, SEM, EDS and XRD as well as mechanical testing. The results show that the as-sprayed billet has an equiaxed and homogeneous structure with grain sizes of 20-40μm and without macro-segregation. After indirect extrusion and T76 heat treatment, the billets were fully densified with a certain amount of recrystallized grains. The ultimate tensile strength of the alloy after T76 heat treatment reaches 680MPa with 10% elongation.
The segregation of solute atoms in hot rolled LT24 aluminum alloy was investigated by atom probe tomography. The results show that a precipitate with composition of Al0.5Mg(Si0.7Cu0.3) can be observed in the grains. No solute segregation can be observed at the interface between precipitates and the matrix. However solute atoms, such as Mg, Si and Cu all tend to segregate at grain boundaries, but the segregation tendency of Cu is much stronger than that of Mg and Si. The concentration of Cu at grain boundaries is 45 times of that at the matrix. Based on the experimental results, the feature of solute segregation and its effect on the performance of the alloy are discussed.
Bentonite was modified by means of ion exchange with two Gemini surfactants (1, 3-bis(dodecyldimethylammonio)-propane dibromide (BDP) and 1, 3-bis(dodecyldimethylammonio)-2-hydroxypropane dichloride (BDHP)) respectively to prepare two organ- bentonites BDP-B and BDHP-Bt. The organ-bentonites were characterized by X-ray diffraction (XRD) and FT-IR spectroscopy. Then their adsorption ability of phenol from aqueous solutions was examined in terms of the pH value and contact time. The results show that the adsorption of phenol increases with of the increasing pH value. The adsorption kinetics was found to follow the pseudo-second-order kinetic model and the equilibrium data fitted the Langmuir and Temkin equations better than Freundlich equation for both BDP modified bentonite (BDP-Bt) and BDHP modified bentonite (BDHP-Bt). The results also show that BDHP-Bt containing one hydroxyl in the Gemini surfactant molecule was more effective than BDP-Bt for the sorption of phenol from aqueous solutions. Thus, a new idea was put forward for the selection of high efficient modified agent, i.e., hydroxyl-containing Gemini surfactants. The negative values of ΔG° and ΔH° obtained from thermodynamic study of adsorption process indicated the spontaneous and exothermic nature for the two organ- bentonites.
Spherical Cr2O3 nanoparticles of 10-20 nm in diameter were prepared by combustion method. Then the effect of Cr2O3 particles addition on the corrosion resistance of epoxy coatings applied on hot-dip galvanized steel sheet was investigated by electrochemical impedance spectroscopy (EIS) and salt-spray tests. The results show that the addition of Cr2O3 particles can significantly enhance the corrosion resistance of epoxy coatings, because the addition of Cr2O3 particles results in decreasing the porosity and increasing the physical shielding function of the coatings. And Cr3+ may react with Zn2+ and OH- in the corrosive medium, produce insoluble ZnCr2O4 barrier film.
Polyurethane foams based on guluronic acid (G)-rich sodium alginate (PF-SA) were synthesized by using cross-linking low molecular weight G-rich alginic acid(LG-HA)with hexamethylene diisocyanate (HDI). The prepared PF-SA was characterized and its adsorption performance of methylene blue (MB) in aqueous solution was investigated by XRD, FTIR, SEM, BET. The results show that the dosage of HDI and the concentration of LG-HA have a significant impact on the morphology and the microstructure of PF-SA; PF-SA with three-dimensional interconnected pore structure may be prepared when the molar ratio of HDI to the monomer unit of LG-HA was in the range of 1: 4 to1: 3, the concentration of LG-HA was in the range of 0.08-0.1 g/mL; this PF-SA is effective for the adsorption of MB: for a solution with concentration of 100 mg/L MB, the adsorption equilibrium can be reached in 30-160 min at room temperature. The removal efficiency of MB was as high as 99%．
FePO4·H2O precursor was synthesized by the co-precipitation method from raw materials Fe (NO3)3·9H2O, H3PO4 and NH3·H2O, which then was modified by surfactants hexadecyl trim ethyl ammonium bromide (CTAB) and polyethylene glycol (PEG). Finally LiFePO4 /C composites were synthesized with the as-prepared FePO4·2H2O, Li2CO3 and sucrose as raw materials. The LiFePO4 /C composites were characterized by means of X-ray diffractormeter (XRD) and scanning electron microscope (SEM). Their performance was determined by cyclic voltammograms (CV) and electrochemical measurement.. The results show that the presence of surfactants CTAB and PEG may be beneficial to suppressing the agglomeration of the particles of the composites; thereby their electrochemical properties were enhanced. The LiFePO4/C particles synthesized with surfactant CTAB modified FePO42H2O exhibit excellent dispersive ability with particle mean size 170nm and excellent cycle performance and rate properties i.e. a discharge specific capacity 159.8 mAhg-1 at 0.1C as well as a value higher than 132.4 mAhg-1 even at 10C.
The influence of Fe content and particle size of carbonyl iron powder on shear yield stress of magnetorheological fluids were investigated. The results show that the max shear yield stress of magnetorheological fluids with different carrier oil increases with the increasing Fe content, as well as the increasing particle size respectively. A formula is deduced to assess the weight factor related with the effect of Fe content and particle size on the performance of MRF, which was then optimal through experimental approach. It follows that the Fe content of carbonyl iron powder weighs higher than the particle size in terms of their contribution to the enhancement of shear yield stress. In the end, the possible errors have been analyzed, so that to prove the validity of experiments carried out above.
